In general, high impact polystyrene (HIPS) resins can have excellent mechanical strength and extrusion and injection workability and thus are used for interior and exterior materials of electric and electronic appliances. However, HIPS resins have poor flame resistance and can expand and sustain combustion since the resins themselves are decomposed when ignited. Due to increased social concerns and standardized fire safety requirements, there is an increasing need to manufacture flame-retardant exterior materials for electric and electronic appliances.
One method for imparting flame retardancy to HIPS resins includes adding flame retardants containing inert elements, such as halogen, phosphorous and the like, and flame retarding aids to the HIPS resins. As an example, halogen-containing organic compounds and antimony-containing inorganic compounds can be mixed with high impact polystyrene resins to impart flame retardancy to the resin. Halogen-containing organic compounds typically used include decabromodiphenyl ether, decabromodiphenyl oxide, decabromodiphenyl ethane, tetrabromobisphenol A, brominated epoxy oligomers, hexabromocyclododecane, 2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5-triazine, and the like.
However, in order to obtain UL94 V-0 ratings, excessive amounts of halogen compounds and antimony trioxide should be added to the HIPS resins. This can, however, deteriorate mechanical properties and fluidity of the HIPS resins. For example, brominated epoxy oligomers are substantially incompatible with high impact polystyrene resins and can thereby lower mechanical properties such as impact strength, even though higher molecular weight brominated epoxy oligomers can increase heat resistance. Decabromodiphenyl ethane can lower impact strength and fluidity of a resin composition and make a final resin product opaque due to its high melting point and lack of dispersibility in the resins. Further, 2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5-triazine is not desirable from an environmental aspect since it is prepared using tri-bromophenol.